Progress in an endoscopic examination has enabled detection of a mucosa tumor in a lumen such as a digestive tract. A great number of mucosal resections have been carried out to ablate a mucosa tissue from a muscle tissue under a mucosa to remove the mucosa tissue endoscopically using a treatment tool such as a diathermy knife. Yet, if an endoscopic submucosal resection is carried out to peel and resect the mucosa of a wide area at once, a problem occurs in the resection when the mucosa peeled and ablated covers a site to be ablated from a muscle layer. Blind ablation is necessary in this case, thus increasing risk of occurrence of perforation of the digestive tract and the like if the treatment tool such as the diathermy knife injures the muscle layer.
Efficient ablation of the mucosa in the wide area requires that the diathermy knife and the like be put on a boundary between the mucosa and the muscle layer while tensile force is applied in a direction in which the ablated mucosa peels from the muscle layer. Nevertheless, many endoscopes are provided with only one forceps aperture for allowing the treatment tool such as the diathermy knife to pass. The forceps aperture of the endoscope has thus no space for allowing the size larger than that of the diathermy knife and the like to pass. As a result, a problem exists where grasping forceps and the like are unavailable to apply the tensile force to a living tissue such as the mucosa.
Disclosed is an endoscope hood configured to be mounted on a tip end of the endoscope, the endoscope hood aiming to prevent the blind ablation described above in the endoscopic submucosal resection and the like (See Patent Document 1, for example). The endoscope hood has the tip end provided with a projection so as to ensure a predetermined distance between the tip end of the endoscope (object lens) and a treatment site. The treatment site is thus observable in an excellent manner. Still, a problem exists where the endoscope hood has difficulty in getting between the mucosa and the muscle layer, because the endoscope hood itself has a straight-cylindrical shape in a longitudinal axis direction. Accordingly, a problem exits where it is difficult to apply the tensile force for peeling the ablated mucosa from the muscle layer.
Also disclosed is the endoscope hood tapering off toward the tip end side (See Patent Document 2, for example). In the endoscope hood, the object lens on the tip end of the endoscope is arranged eccentrically with respect to a central axis of the endoscope. That is to say, a tip end side opening of the endoscope hood has a central axis formed eccentrically so that the central axis of the tip end side opening substantially conforms to a central axis of the object lens. As a result, a problem exists where a linear route cannot be secured from a treatment tool outlet port on the tip end of the endoscope to the treatment site, and operability of the treatment tool such as the diathermy knife deteriorates.